I'm experiencing booting problem with a custom built desktop that was given to me without OP install. I installed Win 7 - no problem booting, but ran very slowly. So I upgraded Win 8.1 and that's where the booting problem started - but OK once booted and runs faster than when win7 was installed. I tried re-seating RAM, battery and check all cable connection from CPU to motherboard, HD, etc., and updated all drivers, but problem's still there.